Various photographic techniques using radiopaque or radiation-impermeable contrast media have been proposed. For instance, in the field of angiography using X-rays, the direct-film method, X-ray cinefilm method, and digital subtraction method are known.
The proposed techniques are all relied on a system in which two-dimensional serial photographing from a fixed angle is achieved with injection of an intravascular radiopaque contrast medium. Due to the fixed photographing angle, this system is in many case unable to make a correct diagnosis, e.g. of the extent and site of a coronary stricture (focus responsible for the disease) of the acute myocardial infarction based on a single run of the serial photographing, and subsequently take an appropriate therapeutic treatment, such as PTCA (Percutaneous Transluminal Coronary Angioplasty) without delay. Particularly when the object to be examined is in the dynamic state or in motion, such a fixed-position photographing is almost unable to detect the condition of a portion of the object opposite the view site.
In order to obtain correct information about the object, observation of additional images taken from many different angles is inevitable. Such a multi-angle observation, however, requires repeated photographing entailing synchronous repeated injection of the contrast medium with the resultant prolonged examination time and increased medical radiation exposure.
There have been proposed techniques related to the serial rotation stereography in which a stereoscope is used to observe an image as a stereograph from a desired position. The proposed techniques include special two trains of electronic circuits additionally provided to display analog images or digital subtraction images with predetermined angular phases on two display units, e.g., television monitors (see, Japanese Patent Laid-open Publications Nos. 61-159941 and 2-156778, for example).
The proposed techniques are, however, not available for the simultaneous stereoscopic observation by multiple viewers, nor avails no function thereof against the viewer having an artificial eye. Further, for a viewer who is amblyopic or has visual acuity imbalance, observation itself is complicated and might lead to a severe ocular fatigue.
The photographing technique used in the known serial rotation stereograph apparatus requires 10 sec or more for photographing each unit angle of rotation. In the case where an object to be examined is in motion, such as the left ventricle of an adult heart (though varying with the organs), a 40 cc intravascular contrast medium is forced out from the heart in a short period of time by the blood flow, so that the photographing angle per single injection of the contrast medium is limited to 30.degree. at maximum. In order to photograph the entire 360.degree., a great amount of intravascular contrast medium must be injected with the result that the object is subjected to undue load. Accordingly, the intended observation of serial or continual photographing conditions is practically impossible.
The prior technique disclosed in Japanese Patent Laid-open Publication No. 61-159941 gives no consideration to the time point when the injected contrast medium images in the object is photographed, and to the manner in which the contrast medium is injected toward a predetermined affected part. Accordingly, there is a risk of the injected contrast medium images at a predetermined portion being photographed inaccurately. In addition, the contrast medium is discharged from the object in a short period of time, as previously described, so the photographing necessarily involves repeated injection of the contrast medium.
In order to avoid halation on a recorded frame image, the use of a filter is inevitable. The fixed filter, when used, must be displaced according to the photographing angle, so that the photographing device has a limitation in its rotation speed.
Stated more specifically, when the photographing apparatus rotates about an object held stationary and having a vertical size (thickness) different from a horizontal size (width), due partly to the difference between the vertical size and the horizontal size of the object, and partly to the rotation of the photographing apparatus, the amount of radiation penetrating through the object is caused to change abruptly at a relatively thin or narrow portion of the object and at an air-containing organ of the object such as lungs, thus causing a halation. In order to prevent the halation, the filter must be displaced in view of the relation between the angular position of the photographing apparatus and the object.
However, since the conventional filters are so constructed as to block unnecessary radiation by means of a clay plate of copper or zinc, they can only deal with an application in which a predetermined field of view is two dimensionally photographed from a predetermined direction with the filter is disposed in a predetermined position (for filtering). When different portions of the same object to be photographed or when the photographing apparatus is rotated, the position of the filter must be changed.
For example, when an abdominal X-ray examination of an object is intended, it is sufficient to previously place a filter well matched in shape and structure with the abdomen of the object. However, when objects to be examined have different abdominal shapes, or when the X-ray examination must be achieved in a fixed time period with respect to both abdomen and chest of the object, the intended X-ray examination cannot be achieved only with the use of a filter disposed to filter the abdominal part. For the chest X-ray examination, the filter must be displaced in position, which displacement is conventionally effected manually with continual observation under the X-ray fluoroscopy.
The manual filtering operation under X-ray fluoroscopic observation is complicated, prolongs the fluoroscoping time and increases the radiation exposure. To overcome these deficiencies, an automatic filtering technique called auto-iris has been proposed.
In the operation of the auto-iris, the distribution of halation varying with the location or site is detected by a sensor to displace the filter to an appropriate filtering position. In despite of the use of the auto-iris, it takes 10 sec or more to turn the photographing apparatus to 180.degree. for photographing an object. Due to this long photographing time, re-injection of the contrast medium is unavoidable, and emission of the pulsed radiation proportional to the photographing time is needed. More particularly, the auto-iris has a critical problem that it cannot deal with high-speed rotation of the photographing apparatus, and the filter has a constant thickness and hence is not adaptable to those objects having different thicknesses or widths.
In the case where a certain portion of a predetermined part of an object is to be continuously photographed by a photographing apparatus fixed at a predetermined angle, an angle to be observed must be found out first to determine the predetermined angle. Thus, the portion to be continuously photographed can not be found out unless multilateral photographing completes in advance.
Furthermore, in the case where the object to be examined is in motion like the heart and entails bleeding from a blood vessel, the conventional photographing time of more than 10 sec for 180.degree. does not ensure observation of actual, continual bleeding condition (functioning condition) of the moving object, but only enables observation of sham dynamic images taken intermittently at regular intervals of time. It is, therefore, extremely difficult to make a precision diagnostic examination of the side and extent of the functioning condition.
Even if the images taken at a low speed are observed in the high-speed serial display mode, observed images are still far different from actual images with the result that observation of the actual continual dynamic condition (live images) on the real-time basis is still unachievable.
The rotation speed and the photographing time of the radiographic apparatus are important factors to improve the clinical usefulness. This is because in the angiocardiography, aortography, cavography, pulmonary angiography, coronary arteriography, and angiography for other great vessels, a correct diagnosis can be pronounced by virtue of three-dimensional or stereoscopic understanding of the form and structure of blood vessels and observation of the function and blood flow condition.
To this end, in the case of the heart, for example, observation should preferably be achieved at high speeds under the condition that a single stroke of diastolic and systolic phases (one heartbeat) of the heart is observed in a predetermined angle ranging from 10.degree. to 90.degree., and preferably from 30.degree. to 50.degree., the predetermined heart rate is at least 2 to 6, and preferably about 4; and the rotation angle is 360.degree. or several times greater than 180.degree..
In the prior art, no consideration is given to the one-heartbeat observation angle, the rotation angle, and rotation photographing time synchronized with the heart rate of an object to be examined. Particularly, in the angiography of an object consisting of heart and great vessels or a solid organ, no account is taken on the peculiarity of photographing conditions. Namely, in the case of the angiocardiography or the solid organ angiography, the peculiarity of the object is left out of consideration.
The prior art is generally limited to a continuous photographing over an angle of 180.degree. extending from the left side to the right side, and when it is used in the angiography, angiographic images in the range of 180.degree. can be obtained. However, when the angiography is started from an arbitrary angle .alpha..degree., it is only possible to obtain images in an angular range of 180.degree.-.alpha..degree. because the maximum photographing angular range is 180.degree., as described above.
This is partly because the photographing apparatus according to prior art do not rely on the standpoint of photographing live images at high speeds as in the present invention, but aim at a solution of the problems associated with low-speed photography over an angle of 180.degree., and partly because the prior filters are only adaptable to the photographing range of 180.degree..
In the case where an object to be examined is cardiac great vessels, and particularly when an intravascular contrast medium is injected into the right atrium for image formation, the prior art having a photographing angular range of 180.degree. cannot perform the serial rotation imaging of a system composed in sequence of vena cavae-right atrium-right ventricle-pulmonary artery-pulmonary veins-left ventricle-left atrium-aorta-peripheral vessels-vena cavae, along the direction of flow of the contrast medium. This is also true in the angiography of solid organs represented by carcinomas.
In the prior technique using digital subtraction (Japanese Patent Laid-open Publication No. 2-156778, for example), mask images are photographed and these mask images and contrast medium images are subtracted. However, since the contrast medium images are sham dynamic images taken intermittently at regular intervals of time, this prior technique has a critical drawback that even if the images taken at a low speed are merely observed in the high speed continuous display mode, the observed images are still far different from actual images.
The prior art still has problems left unsettled: the disadvantage inflicted on an object or patient due to the medical radiation exposure, and the dose-dependent side effect of the radiopaque contrast medium. That is, a radiographic observation accompanying a great dose of radiopaque contrast medium necessarily involves a medical radiation exposure injury concentrated particularly at the gonad, bone marrow and thyroid gland.
The present inventors conceived the present invention through diligent researches in the subjects of: a filter adaptable for the serial high-speed rotatography; stereoscopic or three-dimensional understanding of the form and structure of an object and serial photography of the actual dynamic condition; serial or continuous photographing of the function and blood flow condition of the object (live-image photographing); photographing the object in a short period of time from every possible angle without forming a dead angle with a single injection of usual dose of a radiopaque contrast medium for reducing the radiation exposure and the dose of the radiopaque contrast medium; photographing from an arbitrary angle over an optimal angular range; photographing over the entire 360.degree. starting from any angular position; and three-dimensional understanding of the object and precision diagnostic examination of the object made correctly on the real-time basis in terms of the distance, area and volume.
It is accordingly an object of the present invention to provide a K-filter which is suitable for the serial high-speed rotatography and capable of achieving a desired filtering operation even when a photographing apparatus turns 180.degree. or more or 360.degree. from an arbitrary position.
Another object of the present invention is to provide an apparatus for the serial high-speed rotatography, which is capable of continuously photographing the actual dynamic state of an object in a short period of time by carrying out the serial high-speed rotatography.
A further object of the present invention is to provide a serial high-speed rotatograph apparatus which is capable of photographing an object in a short time from an arbitrary angle without forming a dead angle and accompanying only a single dose or injection of a radiopaque contrast medium, thus reducing the radiation exposure and the amount of radiopaque contrast medium used.
Still another object of the present invention is to provide an serial high-speed rotatograph apparatus which is capable of determining an optimal photographing time for the rotatography of each of different objects susceptible to influences from the heart rate, which is capable of photographing an image to enable stereoscopic understanding of the form and structure of the object, and which is able to continuously photographing the function and blood flow condition of the object.
Yet another object of the present invention is to provide a serial high-speed rotatograph apparatus which is capable of achieving photographing from an arbitrary angle within an optimal angular range in accordance with the heart rate.